High power electrically variable inductor

ABSTRACT

A high power electrically variable inductor includes a U-shaped ferrite core with an electromagnet and a permanent magnet attached to the U-core. The RF variable inductor winding is wound on a multiplicity of separate sections of the U-core. The area of the ferrite material at the RF winding is reduced to minimize the DC magnetic field.

United States Patent Sinnott et al.

[ May 22, 1973 HIGH POWER ELECTRICALLY VARIABLE INDUCTOR Inventors:Norbert C. Sinnott, Adelphi, Mdx, Harold A. Jones, Jr., Thousand Oaks,Calif.

Assignee: The United States of America as represented by the Secretaryof the Air Force, Washington, DC.

Filed: Sept. 20, 1972 Appl. No.: 290,603

U.S. Cl. ..336/1 10, 336/160, 336/172, 336/212 Int. Cl ..I-I01f 21/00Field of Search ..336/1l0, 155, 160, 336/172, 212, 214, 215

[56] References Cited FOREIGN PATENTS OR APPLICATIONS 763,497 12/1956Great Britain ..336/l10 Primary Examiner-Thomas J. Kozma Att0rneyHarryA. Herbert, Jr. et a1.

[5 7] ABSTRACT A high power electrically variable inductor includes aU-shaped ferrite core with an electromagnet and a permanent magnetattached to the U-core. The RF variable inductor winding is wound on amultiplicity of separate sections of the U-core. The area of the ferritematerial at the RF winding is reduced to minimize the DC magnetic field.

2 Claims, 2 Drawing Figures Patented May 22, 1973 HIGH POWERELECTRICALLY VARIABLE INDUCTOR BACKGROUND OF THE INVENTION In the priorart, there is utilized high frequency saturable-core magnetic apparatusin which the inductance of a signal winding is controlled by varying themagnitude of a current through a control winding. In such magneticcontrol devices, called controllable or variable inductors, the controland signal windings are wound on portions of the same or magneticallyinterconnected ferromagnetic core structures. Variations in the currentflowing through the control windings changes the degree of magneticsaturation of desired portions of the core structure, so varies theeffective inductance of the signal winding. Thus, the magnitude ofalternative current passed through the signal winding can be controlledin accordance with variations produced in the control current flowingthrough the control winding.

One of the uses of saturable-core magnetic devices exists in automatictuning systems, for example, in tuning systems for HF or VHF poweramplifiers or antennas. However, this requires high power electricallyvariable inductors and the prior art devices have limitations as to RFpower handling capability of the RF inductor. Another limitation residesin the DC power requirements for the control winding. The presentinvention improves substantially the power handling capability of the RFinductor while simultaneously decreasing the DC power requirement of thecontrol winding. Another advantage of the device of the presentinvention is its rapid tuning ability.

SUMMARY OF THE INVENTION A high power electrically variable inductor isprovided. It is comprised of a U-shaped ferrite core with anelectromagnet and permanent magnet attached to the U-core. A balanced RFvariable inductor winding is wound on three (or more) separate sectionsof the U-core. The area of the ferrite material at the RF winding isreduced to minimize the DC magnetic field required for permeabilitytuning. A permanent magnet biases the ferrite material in the RF windingregion to a lower permeability, higher Q state thus making possiblelower RF loss. Increasing DC current in the electromagnet decreases thepermeability further which changes the RF inductance.

DESCRIPTION OF THE DRAWINGS FIG. 1 shows a front view of the preferredembodiment excluding an RF inductor winding and shunt permanent magnet;and

FIG. 2 shows the side view of FIG. 1 including the RF inductor windingand shunt permanent magnet.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Now referring in detailto FIG. 1, there is shown U- shaped ferrite core 10 which is readilysaturable. The area of U-shaped ferrite core 10 has been substantiallyreduced at sections 10a, 10b, and 10c. I-Ioles 10d, le, and f have alsobeen provided through U-shaped ferrite core 10 at sections 10a, 10b, and100, respectively. The RF inductor winding (not shown in FIG. 1) iswound utilizing sections 10a, 10b, and 100, and associated holes 10e,10f, and 10d, respectively. Magnet steel bar 1 l is attached to ends 12and 13 of U-shaped ferrite core 10 by any suitable conventional means.Coil 14 is wound around magnet steel bar 11. Electromagnetic coil 14 isprovided with terminals 15 which receives a variable DC input from anyconventional source and operates as a control winding.

Referring to FIG. 2, there is shown a side view of FIG. 1 in which RFvariable inductor winding 16 is clearly illustrated. Terminal 17 thereofreceives the RF input signal and terminal 18 provides the RF outputsignal. Permanent magnet bar 19 is shown and may be attached by anysuitable conventional means to U-shaped ferrite core 10. Bar 19 servesas a shunt magnet.

RF variable inductor winding 16 is a balanced winding. Equal number ofturns appear on opposite sides of each of holes 10d, 10e, and 10f. Threeseparate winding sections are series connected to form RF variableinductor 16 and is as illustrated in sections 10a, 10b, and 100, andassociated holes 10d, Ne, and 10f, respectively. The area of the ferritematerial at sections 10a, 10b, and 10 thus at the RF winding has beensubstantially reduced to minimize the DC magnetic field required forpermeability tuning. Permanent magnet bar 19 biases the ferrite materialin the RF winding region to a lower permeability, higher Q (lower RFloss), state. Increasing DC current in the electromagnet decreases thepermeability still further which changes the RF inductance.

In the configuration shown in FIGS. 1 and 2, a 4 to 1 change in RFinductance with Q greater than over the entire range can be obtainedwith 1 watt of DC power used by the electromagnet for tuning. Inaddition, the RF induction can handle 320 volt-amperes (p It isemphasized that the use of a shunt permanent magnet reduces the requiredmagnet DC tuning power. Still further, the series connection of threesections of the RF inductor, all of which are tuned by the sameelectromagnet increases the RF power handling capability of the RFinductor while reducing the required electromagnet tuning power.

It is claimed:

1. A high power electrically variable inductor comprising a U-shapedferrite core having two arms, and a connecting member, said connectingmember having first, second, and third sections with substantiallyreduced areas to minimize the DC magnetic field, each of said sectionsalso having holes therethrough, a balanced RF variable inductor windingconsisting of three series connected portions, each of said portionshaving an equal number of turns on opposite sides of the associated holeand wound on the associated section thereof, said balanced RF variableinductor winding including an input terminal for the reception of a highpower RF input signal and an output terminal providing a high power RFoutput signal, an electromagnet attached across the ends of said twoarms closing said U- shaped ferrite core, said electromagnet receiving avarying DC input signal thus operating to vary the magnitude of theinductance of said balanced RF variable inductor winding, and a shuntpermanent magnet also attached to said U-shaped ferrite core biasing theferrite material in the RF variable inductor winding region to a lowerpermeability.

2. A high power electrically variable inductor as de scribed in claim 1wherein said electromagnet is comprised of a magnet steel bar and anelectromagnet coil wound thereon.

1. A high power electrically variable inductor comprising a Ushapedferrite core having two arms, and a connecting member, said connectingmember having first, second, and third sections with substantiallyreduced areas to minimize the DC magnetic field, each of said sectionsalso having holes therethrough, a balanced RF variable inductor windingconsisting of three series connected portions, each of said portionshaving an equal number of turns on opposite sides of the associated holeand wound on the associated section thereof, said balanced RF variableinductor winding including an input terminal for the reception of a highpower RF input signal and an output terminal providing a high power RFoutput signal, an electromagnet attached across the ends of said twoarms closing said U-shaped ferrite core, said electromagnet receiving avarying DC input signal thus operating to vary the magnitude of theinductance of said balanced RF variable inductor winding, and a shuntpermanent magnet also attached to said U-shaped ferrite core biasing theferrite material in the RF variable inductor winding region to a lowerpermeability.
 2. A high power electrically variable inductor asdescribed in claim 1 wherein said electromagnet is comprised of a magnetsteel bar and an electromagnet coil wound thereon.